Chapter 6. Hearing, Balance, Taste, and Smell
Follow us on Facebook and Twitter, or subscribe to our mailing list, to receive news updates. Learn more.
By Emily DeMarco For owners of picky cats, that disdainful sniff—signaling the refusal of yet another Friskies flavor—can be soul-crushing. Some cats are notoriously finicky eaters, but the reasons behind such fussy behavior remain fuzzy. Previous research has shown that cats can’t taste sweet flavors, but little is known about how they perceive bitter tastes. Now, researchers in the pet food industry have identified two bitter taste receptors in domestic cats, which could help explain why some felines are so choosy when it comes to their chow. In the study, published today in BMC Neuroscience, the scientists used cell-based experiments to see how the two cat taste receptors, known as Tas2r38 and Tas2r43, responded to bitter compounds such as phenylthiocarbamide (PTC) and 6-n-propylthiouracil (PROP)—which have molecular structures similar to ones in Brussels sprouts and broccoli—as well as aloin (from the aloe plant) and denatonium (used to prevent inadvertent ingestion of some chemicals). When compared with the human versions of these receptors, the researchers found that the cat bitter receptor Tas2r38 was less sensitive to PTC and did not respond to PROP, whereas Tas2r43 was less sensitive to aloin but more sensitive to denatonium, leading the researchers to conclude that cats taste different, and perhaps more narrow, ranges of bitter flavors than humans. The research could help pharmaceutical and pet food manufacturers create compounds that block or inhibit these bitter taste receptors, the team says, potentially leading to more appetizing medicines (if such a thing exists) and foods for our feline companions. © 2015 American Association for the Advancement of Science
Lauren Silverman Jiya Bavishi was born deaf. For five years, she couldn't hear and she couldn't speak at all. But when I first meet her, all she wants to do is say hello. The 6-year-old is bouncing around the room at her speech therapy session in Dallas. She's wearing a bright pink top; her tiny gold earrings flash as she waves her arms. "Hi," she says, and then uses sign language to ask who I am and talk about the ice cream her father bought for her. Jiya is taking part in a clinical trial testing a new hearing technology. At 12 months, she was given a cochlear implant. These surgically implanted devices send signals directly to the nerves used to hear. But cochlear implants don't work for everyone, and they didn't work for Jiya. A schoolboy with a cochlear implant listens to his teacher during lessons at a school for the hearing impaired in Germany. The implants have dramatically changed the way deaf children learn and transition out of schools for the deaf and into classrooms with non-disabled students. "The physician was able to get all of the electrodes into her cochlea," says Linda Daniel, a certified auditory-verbal therapist and rehabilitative audiologist with HEAR, a rehabilitation clinic in Dallas. Daniel has been working with Jiya since she was a baby. "However, you have to have a sufficient or healthy auditory nerve to connect the cochlea and the electrodes up to the brainstem." But Jiya's connection between the cochlea and the brainstem was too thin. There was no way for sounds to make that final leg of the journey and reach her brain. © 2015 NPR
By Meeri Kim The dangers of concussions, caused by traumatic stretching and damage to nerve cells in the brain that lead to dizziness, nausea and headache, has been well documented. But ear damage that is sometimes caused by a head injury has symptoms so similar to the signs of a concussion that doctors may misdiagnose it and administer the wrong treatment. A perilymph fistula is a tear or defect in the small, thin membranes that normally separate the air-filled middle ear from the inner ear, which is filled with a fluid called perilymph. When a fistula forms, tiny amounts of this fluid leak out of the inner ear, an organ crucial not only for hearing but also for balance. Losing even a few small drops of perilymph leaves people disoriented, nauseous and often with a splitting headache, vertigo and memory loss. While most people with a concussion recover within a few days, a perilymph fistula can leave a person disabled for months. There is some controversy around perilymph fistula due to its difficulty of diagnosis — the leak is not directly observable, but rather identified by its symptoms. However, it is generally accepted as a real condition by otolaryngologists and sports physicians, and typically known to follow a traumatic event. But concussions — as well as post-concussion syndrome, which is marked by dizziness, headache and other symptoms that can last even a year after the initial blow — also occur as the result of such an injury.
By SINDYA N. BHANOO Male Java sparrows are songbirds — and, scientists reported on Wednesday, natural percussionists. The sparrows click their bills against a hard surface while singing. That clicking is done in coordination with the song, much as a percussion instrument accompanies a melody. Researchers at Hokkaido University in Japan observed the birds producing clicks frequently toward the beginning of their songs and around specific notes. Birds that were related produced similar percussive patterns, but whether this behavior is learned or innate is unclear. Next the scientists, who described their findings on Wednesday in the journal PLOS One, would like to know whether male sparrows use bill clicks during courtship communication. © 2015 The New York Times Company
Jon Hamilton When Sam Swiller used hearing aids, his musical tastes ran to AC/DC and Nirvana – loud bands with lots of drums and bass. But after Swiller got a cochlear implant in 2005, he found that sort of music less appealing. "I was getting pushed away from sounds I used to love," he says, "but also being more attracted to sounds that I never appreciated before." So he began listening to folk and alternative music, including the Icelandic singer Bjork. There are lots of stories like this among people who get cochlear implants. And there's a good reason. A cochlear implant isn't just a fancy hearing aid. When his cochlear implant was first switched on, the world sounded different. "A hearing aid is really just an amplifier," says Jessica Phillips-Silver, a neuroscience researcher at Georgetown University. "The cochlear implant is actually bypassing the damaged part of the ear and delivering electrical impulses directly to the auditory nerve." As a result, the experience of listening to music or any other sound through the ear, with or without a hearing aid, can be completely unlike the experience of listening through a cochlear implant. "You're basically remapping the audio world," Swiller says. Swiller is 39 years old and lives in Washington, D.C. He was born with an inherited disorder that caused him to lose much of his hearing by his first birthday. That was in the 1970s, and cochlear implants were still considered experimental devices. So Swiller got hearing aids. They helped, but Swiller still wasn't hearing what other people were. © 2015 NPR
By Virginia Morell Like humans, dolphins, and a few other animals, North Atlantic right whales (Eubalaena glacialis) have distinctive voices. The usually docile cetaceans utter about half a dozen different calls, but the way in which each one does so is unique. To find out just how unique, researchers from Syracuse University in New York analyzed the “upcalls” of 13 whales whose vocalizations had been collected from suction cup sensors attached to their backs. An upcall is a contact vocalization that lasts about 1 to 2 seconds and rises in frequency, sounding somewhat like a deep-throated cow’s moo. Researchers think the whales use the calls to announce themselves and to “touch base” with others of their kind, they explained in a poster presented today at the Meeting of the Acoustical Society of America in Pittsburgh, Pennsylvania. After analyzing the duration and harmonic frequency of these upcalls, as well as the rate at which the frequencies changed, the scientists found that they could distinguish the voices of each of the 13 whales. They think their discovery will provide a new tool for tracking and monitoring the critically endangered whales, which number about 450 and range primarily from Florida to Newfoundland. © 2015 American Association for the Advancement of Science.
By Chris Cesare For bats, too many echoes can be like blurry vision. That’s because the nocturnal creatures navigate by bouncing ultrasonic sound off of their surroundings, a technique known as echolocation. In cramped spots, these sounds can reverberate, creating a noisy background that clouds the mammals’ sonic sight. Now, new research published online before print in the Proceedings of the National Academy of Sciences has discovered one way that bats might overcome this auditory ambush. Scientists found that the animals modify the width of their navigation pulses on the fly by adjusting the size of their mouth gape. The researchers used an array of cameras, flashes, and ultrasonic recorders to take snapshots of bats while they swooped down to take a sip at a desert pond in Israel. As the bats descended toward the confined banks of the pond, they opened their mouths wider to more tightly focus their sound pulses. As the bats left, they narrowed their mouths, projecting an ultrasonic beam up to four times wider than on the descending leg. These counterintuitive effects were due to diffraction, which causes sound waves traveling through a smaller hole to spread out more. The researchers repeated the experiment with captive bats and found the same effect, controlling for the possibility that they had observed a behavior tied to drinking. The team writes that these changes in gape allow the animals to “zoom in” on their view of an area, potentially reducing the amount of distracting echoes in a tight space. © 2015 American Association for the Advancement of Science
Link ID: 20901 - Posted: 05.09.2015
by Clare Wilson WHAT is it like to be a bat? It's a question philosophers interested in consciousness like to ponder. Yet a few people already have something of a bat's world view. Brian Borowski, a 59-year-old Canadian who was born blind, began teaching himself to echolocate aged 3. He clicks with his tongue or snaps his fingers as he moves about, unconsciously decoding the echoes. Although many blind people get information from sounds around them, few turn this into a supersense by making sounds to help themselves get around. "When I'm walking down a sidewalk and I pass trees, I can hear the tree: the vertical trunk of the tree and maybe the branches above me," says Borowski. "I can hear a person in front of me and go around them." Borowski, who works as a programmer at Western University in London, Ontario, suspects he experiences "images" in a similar way to people who can see, just with less detail. "I store maps of information in my head and I compare what I have in my memory with what I'm hearing around me," he says. "I am matching images of some sort." This probably isn't too far from the truth – we know from brain scans of Borowski and another echolocator that the strategy co-opts the same parts of the brain that usually deal with visual information. For his latest scientific collaboration, he helped a team of researchers to explore how well echolocators can determine the relative sizes and distances of objects. © Copyright Reed Business Information Ltd
Link ID: 20898 - Posted: 05.08.2015
By Paca Thomas Wasabi and Sriracha each activate different receptors on the tongue, both of which warn your brain of the atomic reaction to come. These key flavor receptors, TRPA1 and TRPV1, have been the subject of recent research—but why all the scientific study of hot and spicy condiments? One word: pain. The video above explains how our tongues react to heat in our food, and how that often triggers the body’s own bespoke painkiller.
Keyword: Chemical Senses (Smell & Taste)
Link ID: 20879 - Posted: 05.04.2015
Nala Rogers People who are ill often complain of changes in their sense of taste. Now, researchers report that this sensory shift may be caused by a protein that triggers inflammation. Mice that cannot produce the protein, called tumour necrosis factor-α (TNF-α), are less sensitive to bitter flavours than normal mice, according to a study published on 21 April in Brain, Behavior, and Immunity1. People with infections, autoimmune disease or other inflammatory conditions have higher levels of TNF-α than healthy people, and the protein has been shown to reduce food intake2. To investigate the influence of TNF-α on taste, researchers at the Monell Chemical Senses Center in Philadelphia, Pennsylvania, used engineered mice that could not produce the protein. The researchers offered the engineered mice and normal mice water that contained different types and concentrations of flavours. The mice that could not produce TNF-α had normal reactions to sweet, sour, salty and umami flavours, but were less sensitive to bitter ones. “Normal mice will pick up [that taste] at a much lower concentration. They will know this is bitter; they will not like it,” says Hong Wang, a molecular biologist at Monell and an author of the study. “But if the TNF-α gene is not there, then the mice will only start to avoid the bitter solution at higher concentrations.” © 2015 Nature Publishing Group
By Rachel E. Gross “By being a guy’s best first move … Axe is designed to keep guys a step ahead in the dating game,” boasts Unilever, the company that sells Axe products. Of course, if you don’t happen to be a gullible 13-year-old boy, you probably don’t believe that body spray or deodorant is a magic elixir with the power to turn nice girls naughty. But what if it were possible to change a person’s mood with just a scent? The idea may not be that far-fetched, according to a new study in the journal Psychological Science—reporting work that was funded by Unilever. The study found that it might be possible to subconsciously trigger a state of happiness using the scent of—deep breath now—human sweat. People send all kinds of secret messages through their secretions. When smelling chemicals in male sweat, women become more alert, and they can even tell whether that sweat was made by a guy who was particularly turned on. (Cautions the New York Times: “No man should imagine that based on these conclusions he can improve his sex life by refraining from bathing.”) But until now, most sweat studies have focused on sexual arousal or negative emotions like fear. For obvious reasons, these emotions are crucial to survival and evolutionary success. If your friend spots a puma, it may be helpful for you to be able to sniff out instant cues to be on the alert or flee for cover. Being able to transmit positive emotions may also have a profound social impact, says Gün Semin, a psychologist at Utrecht University in the Netherlands and lead researcher on the study. After all, “the pursuit of happiness is not an individual enterprise,” as he and his fellow researchers write rather eloquently in the new study. So Semin’s team decided to test whether people could communicate happiness via sweat.
By Emily DeMarco Mice and rats communicate in the ultrasonic frequency range, and it’s thought that cats evolved the ability to hear those high-pitched squeaks to better hunt their prey. Now, a new study suggests that sensitivity to higher pitched sounds may cause seizures in some older cats. After receiving reports of the problem, nicknamed the “Tom and Jerry syndrome” because of how the cartoon cat is often startled by sounds, researchers surveyed cat owners and examined their pets’ medical records, looking for insight into the types and durations of seizures and the sounds that provoked them. In 96 cats, they found evidence of the syndrome they call feline audiogenic reflex seizures. The most common types of seizure-eliciting sounds included crinkling tinfoil, clanking a metal spoon on a ceramic feeding bowl, and clinking glass. The severity of the seizure ranged from brief muscle jerks to more serious episodes where the cat lost consciousness and stiffened and jerked for several minutes, the researchers report online today in the Journal of Feline Medicine and Surgery. Both pedigree and nonpedigree cats were susceptible, although one breed was common: Thirty of the 96 cats were Birmans (pictured). Because the seizures coincided with old age—the average age of onset was 15 years—veterinarians could miss the disorder while dealing with the felines’ other health issues, the researchers say. Minimizing exposure to the problematic sounds and preliminary, therapeutic trials with levetiracetam—an anticonvulsant medication used to control epilepsy—among a small sample of the cats seemed to help limit the occurrence of seizures. © 2015 American Association for the Advancement of Science.
by Helen Thomson Tinnitus is the debilitating sensation of a high-pitched noise without any apparent source. It can be permanent or fleeting, and affects at least 25 million people in the US alone. To understand more about the condition, William Sedley at the University of Newcastle, UK, and his colleagues took advantage of a rare opportunity to study brain activity in a man with tinnitus who was undergoing surgery for epilepsy. Surgeons placed recording electrodes in several areas of his brain to identify the source of his seizures. The man – who they knew as Bob (not his real name) – was awake during the procedure, which allowed Sedley's team to manipulate his tinnitus while recording from his brain. First they played him 30 seconds of white noise, which suppressed his tinnitus for about 10 seconds before it gradually returned. Bob was asked to rate the loudness of his tinnitus before the experiment started, as well as immediately after the white noise finished and 10 seconds later. This protocol was then repeated many times over two days. "Normally, studies compare brain activity of people with and without tinnitus using non-invasive techniques," says Sedley. "Not only are these measurements less precise, but the people with tinnitus might be concentrating on the sound, while the ones without tinnitus might be thinking about their lunch." This, he says, can make the results hard to interpret. © Copyright Reed Business Information Ltd
Link ID: 20847 - Posted: 04.25.2015
Hannah Devlin, science correspondent They may stop short of singing The Bells of Saint Mary’s, as demonstrated by the mouse organ in Monty Python, but scientists have discovered that male mice woo females with ultrasonic songs. The study shows for the first time that mouse song varies depending on the context and that male mice have a specific style of vocalisation reserved for when they smell a female in the vicinity. In turn, females appear to be more interested in this specific style of serenade than other types of squeak that male mice produce. “It was surprising to me how much change occurs to these songs in different social contexts, when the songs are thought to be innate,” said Erich Jarvis, who led the work at Duke University in North Carolina. “It is clear that the mouse’s ability to vocalise is a lot more limited than a songbird’s or human’s, and yet it’s remarkable that we can find these differences in song complexity.” The findings place mice in an elite group of animal vocalisers, that was once thought to be limited to birds, whales, and some primates. Mouse song is too high-pitched for the human ear to detect, but when listened to at a lower frequency, it sounds somewhere between birdsong and the noise of clean glass being scrubbed. The Duke University team recorded the male mice when they were roaming around their cages, when they were exposed to the smell of female urine and when they were placed in the presence of a female mouse. They found that males sing louder and more complex songs when they smell a female but don’t see her. By comparison, the songs were longer and simpler when they were directly addressing their potential mate, according to the findings published in Frontiers of Behavioural Neuroscience. © 2015 Guardian News and Media Limited
by Bethany Brookshire Music displays all the harmony and discord the auditory world has to offer. The perfect pair of notes at the end of the Kyrie in Mozart’s Requiem fills churches and concert halls with a single chord of ringing, echoing consonance. Composers such as Arnold Schönberg explored the depths of dissonance — groups of notes that, played together, exist in unstable antagonism, their frequencies crashing and banging against each other. Dissonant chords are difficult to sing and often painful to hear. But they may get less painful with age. As we age, our brains may lose the clear-cut representations of these consonant and dissonant chords, a new study shows. The loss may affect how older people engage with music and shows that age-related hearing loss is more complex than just having to reach for the volume controls. The main mechanism behind age-related hearing loss is the deterioration of the outer hair cells in the cochlea, a coiled structure within our inner ear. When sound waves enter the ear, a membrane vibrates, pulling the hair cells to and fro and kicking off a series of events that produce electrical signals that will be sent onward to the brain. As we age, we lose some of these outer hair cells, and with them goes our ability to hear extremely high frequencies. In a new study, researchers tested how people perceive consonant pairs of musical notes, which are harmonious and generally pleasing, or dissonant ones, which can be harsh and tense. © Society for Science & the Public 2000 - 2015
By Victoria Gill Science reporter, BBC News Researchers in Denmark have revealed how porpoises finely adjust the beams of sound they use to hunt. The animals hunt with clicks and buzzes - detecting the echoes from their prey. This study showed them switching from a narrow to a wide beam of sound - "like adjusting a flashlight" - as they homed in on a fish. Researchers think that other whales and dolphins may use the same technique to trap a fish in their beam of sound in the final phase of an attack. This could help prevent porpoises, whales and dolphins' prey from evading their capture. By revealing these acoustic secrets in detail, researchers are hoping to develop ways to prevent porpoises, and other toothed whales, from becoming trapped in fishing nets. The study, published in the journal eLife, was led by Danuta Wisniewska of Aarhus University. She and her colleagues worked with harbour porpoises in a semi-natural enclosure on the coast of Denmark. "The facility is quite exceptional, " explained Dr Wisniewska. "The animals still have access to the seafloor and are only separated from the harbour by a net. Fish are able to come in, so they're still hunting." In this unique environment, the researchers were able to fit the porpoises with sound-detecting tags, and to place an array of microphones to pick up sound around their enclosure. The team carried out a series of these experiments to work out where the sound energy the porpoises produced was being directed In one experiment, researchers dropped fish into the water to tempt the porpoises to hunt. As echolocating porpoises, whales and dolphins hunt, they switch from an exploratory clicking to a more intense, high frequency buzz - to elicit a continuous echo from the fish they are pursuing. Their beam can be envisaged a cone of sound, said Dr Wisniewska, comparing it to the cone-shaped beam of light from a torch. © 2015 BBC.
Link ID: 20731 - Posted: 03.30.2015
By Virginia Morell Children and parrot and songbird chicks share a rare talent: They can mimic the sounds that adults of their species make. Now, researchers have discovered this vocal learning skill in baby Egyptian fruit bats (Rousettus aegyptiacus, pictured), a highly social species found from Africa to Pakistan. Only a handful of other mammals, including cetaceans and certain insectivorous bats, are vocal learners. The adult fruit bats have a rich vocal repertoire of mouselike squeaks and chatter (listen to a recording here), and the scientists suspected the bat pups had to learn these sounds. To find out, they placed baby bats with their mothers in isolation chambers for 5 months and made video and audio recordings of each pair. Lacking any other adults to vocalize to, the mothers were silent, and their babies made only isolation calls and babbling sounds, the researchers report today in Science Advances. As a control, the team raised another group of bat pups with their mothers and fathers, who chattered to each other. Soon, the control pups’ babbling gave way to specific sounds that matched those of their mothers. But the isolated pups quickly overcame the vocal gap after the scientists united both sets of bats—suggesting that unlike many songbird species (and more like humans), the fruit bats don’t have a limited period for vocal learning. Although the bats’ vocal learning is simple compared with that of humans, it could provide a useful model for understanding the evolution of language, the scientists say. © 2015 American Association for the Advancement of Science
By James Gallagher Health editor, BBC News website, San Diego A dog has been used to sniff out thyroid cancer in people who had not yet been diagnosed, US researchers say. Tests on 34 patients showed an 88% success rate in finding tumours. The team, presenting their findings at the annual meeting of the Endocrine Society, said the animal had an "unbelievable" sense of smell. Cancer Research UK said using dogs would be impractical, but discovering the chemicals the dogs can smell could lead to new tests. The thyroid is a gland in the neck that produces hormones to regulate metabolism. Thyroid tumours are relatively rare and are normally diagnosed by testing hormone levels in the blood and by using a needle to extract cells for testing. Cancers are defective, out-of-control cells. They have their own unique chemistry and release "volatile organic compounds" into the body. The canine approach relies on dogs having 10 times the number of smell receptors as people and being able to pick out the unique smells being released by cancers. The man's best friend approach has already produced promising results in patients with bowel and lung cancers. A team at the University of Arkansas for Medical Sciences (UAMS) had previously showed that a dog could be trained to smell the difference between urine samples of patients with and without thyroid cancer. Frankie the dog Frankie gave the correct diagnosis in 30 out of 34 cases The next step was to see if it could be used as a diagnostic test. Frankie the German Shepherd was trained to lie down when he could smell thyroid cancer in a sample and turn away if the urine was clean.
Keyword: Chemical Senses (Smell & Taste)
Link ID: 20668 - Posted: 03.09.2015
Lights, sound, action: we are constantly learning how to incorporate outside sensations into our reactions in specific situations. In a new study, brain scientists have mapped changes in communication between nerve cells as rats learned to make specific decisions in response to particular sounds. The team then used this map to accurately predict the rats’ reactions. These results add to our understanding of how the brain processes sensations and forms memories to inform behavior. “We’re reading the memories in the brain,” said Anthony Zador, M.D., Ph.D., professor at Cold Spring Harbor Laboratory, New York, and senior author of the study, published in Nature. The work was funded by the National Institutes of Health and led by Qiaojie Xiong, Ph.D., a former postdoctoral researcher in Dr. Zador’s laboratory. “For decades scientists have been trying to map memories in the brain,” said James Gnadt, Ph.D., a program director at the National Institute of Neurological Disorders and Stroke (NINDS), one of the NIH institutes that funded the study. “This study shows that scientists can begin to pinpoint the precise synapses where certain memories form and learning occurs.” The communication points, or synapses, that Dr. Zador’s lab studied were in the striatum, an integrating center located deep inside the brain that is known to play an important role in coordinating the translation of thoughts and sensations into actions. Problems with striatal function are associated with certain neurological disorders such as Huntington’s disease in which affected individuals have severely impaired skill learning.
Tristram Wyatt This Valentine’s Day, like every year, there was a rash of stories in the news about sexy smells and pheromones. You could be forgiven for thinking that human ‘sex pheromones’, in particular the ‘male molecule’ androstadienone, were well established: countless ‘human pheromones’ websites sell it and there are tens of apparently scientific studies on androstadienone published in science journals. These studies are cited hundreds of times and have ended up being treated as fact in books on sexual medicine and even commentary on legislation. The birth place of the pheromone myth was a 1991 conference in Paris sponsored by a US corporation, EROX, which had an interest in patenting androstadienone and another molecule - estratetraenol, from women - as ‘human pheromones’. Unwittingly, leading mammalian olfaction scientists lent the conference credibility. Slotted into the programme and conference proceedings was the short ‘study-zero’ paper on the ‘Effect of putative pheromones on the electrical activity of the human vomeronasal organ and olfactory epithelium’. To my surprise, the authors gave no details at all of how these molecules had been extracted, identified, and tested in bioassays - all routinely required steps in the exhaustive process before any molecule can be shown to be a species-wide chemical signal, a pheromone. Instead there was just a footnote: ‘These putative pheromones were supplied by EROX Corporation’. The missing, essential details were never published. (The claim by EROX-sponsored scientists that adult humans have a functioning vomeronasal organ, against all the evidence, is a story for another day). © 2015 Guardian News and Media Limited